1. Technical Field
The present disclosure relates to a ranging method, in particular, to a ranging method and device considering the statistical value (for example, the standard deviation, i.e. time spread, while considering the noise is the additive white Gaussian noise (AWGN) of the rising time of the received wireless ranging signal due to the noise, and to a location method and device using the ranging method or device.
2. Description of Related Art
The ranging method or device is used to estimate a distance between an object and a ranging device by using a wireless ranging signal. One currently marketed ranging device can detect the signal strength decay of the received wireless ranging signal to estimate the distance between the object and the ranging device, since the wireless ranging signal is attenuated along with the distance ideally. However, the signal strength decay is actually further in response to the channel response, such that this ranging device must obtain the channel response. Since a channel estimator may be required to obtain the channel response, the ranging device for detecting the signal strength decay of the received wireless ranging signal has large cost. Furthermore, if the channel is fast changed (i.e. not a static channel), the estimated distance between the object and the ranging device may have large difference to the actual distance between the object and the ranging device.
Furthermore, strength of received signal can be reasonable reduced by which the objects absorb the electromagnetic wave (EMW) propagated from the transmitter to the receiver. If such object (or objects) are obstructing first Fresnel zone, then level of received signal (radio signal strength, RSSI) is reasonably reduced. Objects which can heavily absorb EMW are thick concrete walls (especially when concrete wall is wet), layers of coal (in coal mines), water, and the similar ones.
As consequence, the distance estimation based on free space propagation model is loaded by big error, wherein the value of the error increases with additional attenuation, reflection, diffusion, diffraction and similar physical effects caused by surrounding objects (these effects are depending on their nature, dimensions, electrical properties, and so on).
Another currently marketed ranging device can calculate or count the trip time of the received wireless ranging signal to estimate the distance between the object and the ranging device, wherein the trip time comprises the rising time of the received wireless ranging signal since the trip time is the time difference between the rising time of the received wireless ranging signal and the rising time of the emitted wireless ranging signal, i.e. the trip time is also called delay time. However, since the channel inevitably has the noise, the rising time of the received wireless ranging signal is spread, i.e. the rising time of the received wireless ranging signal is lengthened. Thus, the estimated distance between the object and the ranging device may be shorter than the actual distance between the object and the ranging device.
Moreover, the location device may use the ranging device, wherein the ranging device is used to estimate the distances between the objects and the ranging device, and the location device can determined the location of the location device according to the estimated distances. Or alternatively, the distances between the object and the ranging devices are estimated by the ranging devices, and the location device can determine the location of the object according to the estimated distances. However, the higher the ranging accuracy of the ranging device is, the higher the location accuracy of the location device is. Thus, a ranging device with a precise accuracy is needed.